1. Field of the Invention
The present invention relates to a fuel vapor processing apparatus.
2. Background Art
Conventionally, to prevent emission of fuel vapor to the atmosphere from a fuel tank of a car, etc., a fuel vapor processing apparatus (hereinafter also called a canister) which temporarily adsorbs fuel components present in fuel vapor is used.
One of such canisters is known (JP-A-2007-146793) which includes: a casing formed with a tank port, a purge port, and an atmospheric air port; four adsorption layers filled with activated carbon and arranged in series inside the casing; and spaces, which are not filled with activated carbon, formed between the adjacent adsorption layers.
In the canister, the temperature significantly falls during purge in an adsorption layer which is close to the atmospheric air port when fuel components are desorbed from the activated carbon filling the adsorption layer. In the canister of the aforementioned conventional technology, in which the distance between the adjacent adsorption layers is insufficient, during purge the gas that decreased in temperature in the adsorption layer close to the atmospheric air port undergoes little increase in temperature in the space which is not filled with activated carbon before flowing into the next adsorption layer. This causes degradation of the desorption performance in the next adsorption layer and insufficient desorption of the fuel components. As a result, a larger amount of fuel components remains in the activated carbon after the purge, so that the fuel components can be blown off to the atmosphere.
In view of this, the present invention aims to provide a fuel vapor processing apparatus which reduces the amount of fuel components remaining in the adsorbing material after purge compared to the conventional canister, and thereby reduces the blow off of fuel components from the atmospheric air port to the outside.
The present invention allows a longer residence time of fuel components in the separation part, compared to the conventional canister, and a larger amount of increase (recovery) in gas temperature which decreased by desorption, since the region is provided on the atmospheric air port side of the main adsorption layer, and in the at least two separation parts provided in the region, when the cross-sectional area of each of the at least two separation parts perpendicular to the flow direction of the passage is converted into a circular cross-sectional area, the distance between the adjacent adsorption layers is larger than the mean value of diameters of the each separation part. Thus, the gas inside the fuel vapor processing apparatus of the present invention can be maintained at a higher temperature during purge compared to the conventional canister. Accordingly, the desorption performance of the adsorbing material can be improved and the amount of fuel components remaining after purge can be reduced compared to the conventional canister, so that the amount of blow off to the atmosphere can be reduced and the blow off suppression performance can be improved.